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Abstract

Enabling solution-based printing techniques for sub-100 nm thin semiconductors for the application in large-area organic electronics is a challenging task. In order to optimize the process parameters, the layers have to be characterized on a large lateral scale while determining the nanometer thickness at the same time. We present a lateral and vertical resolving measurement method for large-area, semi-transparent thin films based on optical interference effects. We analyzed the RGB color images of up to 150 mm square-sized thin film samples obtained by a modified commercial flatbed scanner. Utilizing and comparing theoretical and measured color contrast values, we determined most probable thickness values of the imaged sample area pixel by pixel. Within specific boundary conditions, we found very good agreement between the presented imaging color reflectometry and reference methods. Due to its simple setup, our method is suitable to be implemented as part of a color vision inspection system in in-line printing and coating processes.

Setup of the optical elements and the optical path of the modified commercial flatbed scanner Epson Perfection 3170. BS denotes the beam-splitter which was implemented and Mi the built-in mirrors. Illumination and inspection were adjusted normal to the sample surface.

Measured and normalized spectral radiance I(λ) of the scanner illumination between 380 nm and 780 nm and measured combined spectral transfer functions F́k(λ) for the red, green and blue channel of the scanner.

Table 2 Averaged layer thicknesses of the six labeled fields of Fig. 10 of the printed sample Spiro-MeO-TAD/ITO/glass measured by phase shifting interferometry (PSI) at limited positions at the swiped lines and by the proposed imaging color reflectometry (ICR) of the complete imaged sample area shown in Fig. 7.

Metrics

Table 1

Mean layer thicknesses of the six different SiO2 fields on the Si-wafer measured by spectroscopic ellipsometry (SE) and by the proposed imaging color reflectometry (ICR) based on Fig. 7.

Field ① (nm)

Field ② (nm)

Field ③ (nm)

Field ④ (nm)

Field ⑤ (nm)

Field ⑥ (nm)

SEICR

501.8502.7 ± 0.7

397.4398.6 ± 1.1

298.1298.8 ± 1.0

199.1200.0 ± 1.1

96.398.8 ± 1.5

1.23.4 ± 3.1

Difference

0.9 (0.2%)

1.2 (0.3%)

0.7 (0.2%)

0.9 (0.5%)

2.5 (2.6%)

2.2 (183%)

Table 2

Averaged layer thicknesses of the six labeled fields of Fig. 10 of the printed sample Spiro-MeO-TAD/ITO/glass measured by phase shifting interferometry (PSI) at limited positions at the swiped lines and by the proposed imaging color reflectometry (ICR) of the complete imaged sample area shown in Fig. 7.

Field
(nm)

Field
(nm)

Field
(nm)

Field
(nm)

Field
(nm)

Field
(nm)

PSIICR

22.1 ± 5.722.1 ± 2.4

24.9 ± 5.621.3 ± 3.3

20.2 ± 3.419.0 ± 3.0

19.5 ± 6.618.9 ± 2.7

21.0 ± 4.416.4 ± 1.9

18.4 ± 3.516.5 ± 2.5

Difference

0.0 (0%)

3.6 (14.5%)

1.2 (6.0%)

0.6 (3.1%)

4.6 (21.9%)

1.9 (10.3%)

Tables (2)

Table 1

Mean layer thicknesses of the six different SiO2 fields on the Si-wafer measured by spectroscopic ellipsometry (SE) and by the proposed imaging color reflectometry (ICR) based on Fig. 7.

Field ① (nm)

Field ② (nm)

Field ③ (nm)

Field ④ (nm)

Field ⑤ (nm)

Field ⑥ (nm)

SEICR

501.8502.7 ± 0.7

397.4398.6 ± 1.1

298.1298.8 ± 1.0

199.1200.0 ± 1.1

96.398.8 ± 1.5

1.23.4 ± 3.1

Difference

0.9 (0.2%)

1.2 (0.3%)

0.7 (0.2%)

0.9 (0.5%)

2.5 (2.6%)

2.2 (183%)

Table 2

Averaged layer thicknesses of the six labeled fields of Fig. 10 of the printed sample Spiro-MeO-TAD/ITO/glass measured by phase shifting interferometry (PSI) at limited positions at the swiped lines and by the proposed imaging color reflectometry (ICR) of the complete imaged sample area shown in Fig. 7.